It is highly desirable for various applications to provide steel tubing with a heavy coating of pure aluminum. By way of example, double-wall tubing, such as the well known Bundyweld tubing, shown in Gondek, U.S. Pat. No. 3,957,086, is used in automotive brake lines where it is subject to significant corrosive action by road deicing salts, and to various mechanical hazards and abrasive action. Terne coating (lead-tin alloy) and electrolytic zinc coating historically used for protecting double-wall brake lines, no longer provide sufficient protection because of the greatly increased use of road deicing salts. Brake line tubing is double flared during fabrication, so that any protective coating used must not only be resistant to corrosion and abrasion, but it must also possess outstanding ductility and adhesion. In addition, the condenser coils in air conditioners are generally fabricated from copper tubing to withstand severe corrosive action and for ease of fabrication.
An inexpensive uniform pure aluminum coating with a minimum average thickness of about 0.004 inch (100 .mu.m) meets the stringent current requirements for Bundyweld brake line tubing. Such a coating also renders single-wall steel tubing an attractive alternative to expensive copper tubing for air conditioner condenser coils.